An antistatic pet base film for polarizing plate release film and a method for preparing the same

Abstract

This invention relates to an antistatic PET base film for preparing release films for polarizers and its preparation method. The release film base film is made primarily of optical-grade PET chips, with added modified PET and modified SiO2 fillers of a specific structure. It is produced through co-extrusion casting, a unique three-stage stretching process, and coating with a coating liquid. Specifically, this invention uses optical-grade PET chips as the main material, adds modified PET and modified SiO2 fillers of a specific structure, and prepares a film through co-extrusion casting and a unique three-stage stretching process. Then, an antistatic coating liquid is applied to the film surface. The resulting base film possesses low alignment angle, low lateral thermal shrinkage, and high surface adhesion, while maintaining the high light transmittance and low haze characteristics of optical-grade polyester films and imparting certain antistatic properties. It is particularly suitable for manufacturing release films for high-end polarizers.

Description

Technical Field

[0001] This invention relates to the field of protective film technology for optical display equipment, specifically to an antistatic PET base film for preparing release films for polarizers and its preparation method. Background Technology

[0002] Polarizing films are essential core components for LCD imaging. They consist of a multi-layered composite structure, with the innermost layer being a polyvinyl alcohol (PVA) core layer that polarizes light. On either side are protective layers of cellulose triacetate (TAC), forming the polarizing film substrate. Depending on the application, storage, or transportation requirements, a pressure-sensitive adhesive (PSA) of a certain thickness needs to be coated on one side of the polarizing film substrate, followed by a release film to protect the PSA. On the other side, depending on the product type, a protective film, a reflective film, and a semi-transparent reflective adhesive layer are laminated, thus forming the finished polarizing film.

[0003] Each layer of a polarizer has a specific function. The release film, as a protective layer for the pressure-sensitive adhesive, needs to be peeled off during use, but it must be peeled off without removing the adhesive along with it. Therefore, the release film requires controllable release force and cleanliness. Common raw materials in polarizer release film production include polyester base film and release agent, with the polyester base film being the key material. However, the alignment angle of currently used polyester films is relatively large. During quality monitoring of polarizers, a high alignment angle leads to phase delay and angular shift of light, easily affecting the final test results. Existing technologies have addressed this by reducing the alignment angle of the polyester film, either through process equipment or raw materials, such as CN106433502A, CN113752600A, and CN116694038B. However, while these technologies reduce the alignment angle, they may not fully consider the high thermal dimensional stability (i.e., low shrinkage rate) and high adhesion of the release agent required for the polyester film as the base film. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention starts with the raw materials themselves and combines process improvements to prepare a polyester film that meets the requirements of a release film base film for low thermal shrinkage and high release agent adhesion, while also meeting the requirements of polarizers for low alignment angles. Furthermore, the coating liquid can impart a certain degree of antistatic properties to the film.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing an antistatic PET base film for use in preparing a polarizer release film includes the following steps:

[0007] S1. Weigh and measure the optical-grade PET chips, modified PET, and modified SiO2 filler, place them in a high-speed mixer and mix them, then dry them under vacuum.

[0008] S2. The dried mixture is fed into a single screw extruder, and the extrusion temperature is set to 255~285℃. After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0009] S3. Preheat the cast film to 90℃, perform a first transverse stretching with a stretching ratio of 1.5~2.5 times and a temperature of 95~105℃; then perform a longitudinal stretching with a stretching ratio of 3.2~5 times and a temperature of 105~115℃; perform a second transverse stretching on the longitudinally stretched film with a stretching ratio of 2.5~3.5 times and a temperature of 120~135℃; the three-stage stretching temperature increases progressively, with a total transverse stretching ratio of 3.75~6 times;

[0010] S4. The stretched film is heat-set at 190~220℃ for 5~15s, slowly cooled to 150℃ and held for 10~30min, then cooled to room temperature. An antistatic coating is applied to the film surface, dried at 100~120℃, and finally corona treated; then pulled and wound up; wherein,

[0011] The modified PET is prepared by introducing 2-(pyridin-3-yl) terephthalic acid to replace part of the terephthalic acid during the PET polymerization process, and then blending it with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite and melt extruding it after polymerization.

[0012] The modified SiO2 filler is obtained by free radical polymerization of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide terpolymer grafted onto the surface of KH570 modified SiO2.

[0013] The antistatic coating liquid comprises 70-80 wt% waterborne hydroxy acrylate-polyurethane dispersion, 5-15 wt% ionic liquid antistatic agent, 1-3 wt% curing agent, 0.5-2 wt% accelerator, 0.1-0.5 wt% wetting and leveling agent, and the balance being deionized water.

[0014] Furthermore, the weight fractions of the optical-grade PET chips, modified PET, and nanofillers are 100 parts, 8-15 parts, and 3-8 parts, respectively.

[0015] Furthermore, the preparation process of the 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is as follows:

[0016] Add sodium montmorillonite and deionized water to a beaker, sonicate to disperse it evenly, then transfer it to a water bath and heat it to 60-70℃. While stirring, slowly add 20% by weight of 1-carboxyethyl-3-methylimidazolium chloride of sodium montmorillonite. After the addition is complete, keep it at the temperature for 2-3 hours, filter, wash with water, dry, and grind to obtain the final product.

[0017] Furthermore, the modified PET is prepared by the following method:

[0018] Ethylene glycol and 2-(pyridin-3-yl)terephthalic acid were added to a reactor, and tetrabutyl titanate was added as a catalyst. The temperature was raised to 200-230℃ for esterification. After reacting for 2-3 hours, terephthalic acid was added, and the temperature was raised to 250℃. After reacting for 2-4 hours, antimony glycolate was added as a catalyst. The pressure in the reactor was controlled at 0.3 MPa, and the temperature was raised to 270℃ for 2-3 hours. After the reaction was completed, the product was discharged after natural cooling to obtain poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester. Then, it was mixed with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite in a high-speed mixer until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder to obtain the final product.

[0019] Furthermore, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:10~20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester) to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9~9.5:0.5~1.

[0020] Furthermore, the preparation steps of the modified SiO2 filler are as follows:

[0021] 1) A certain amount of nano-SiO2 particles were first activated with potassium hydroxide, then dispersed in deionized water and an equal mass of KH570 was added. The mixture was stirred at 50°C for 24 hours, filtered, washed, dried and ground to obtain KH570 modified SiO2 powder.

[0022] 2) KH570 modified SiO2 powder was dispersed in THF, and lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide were added in sequence. AIBN of 1% of the total monomer mass was added as an initiator. The reaction was carried out at 70℃ under nitrogen protection for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times with THF to remove the homopolymer. After vacuum drying, the modified SiO2 filler was obtained.

[0023] Furthermore, the molar ratio of lauryl acrylate, glycidyl methacrylate, and N-(4-vinylphenyl)acetamide is 50~70:15~25:15~25; and their total mass is 80%~120% of the KH570 modified SiO2 powder.

[0024] Furthermore, the ionic liquid antistatic agent in the antistatic coating liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt; the curing agent is hydrophilic aliphatic polyisocyanate; the accelerator is KH-560; the wetting and leveling agent is polyether-modified polysiloxane; and the wet coating amount of the antistatic coating liquid is 5~15 g / m². 2 .

[0025] Furthermore, the preparation process of the aqueous hydroxy acrylate-polyurethane dispersion is as follows:

[0026] S1. Preparation of polyurethane prepolymer

[0027] Add 60 parts by weight of polybutylene adipate diol and 10 parts by weight of dimethylolpropionic acid to a reaction flask, add 30 parts by weight of N-methylpyrrolidone as a solvent, purge with nitrogen, heat to 80°C and stir to mix evenly, cool the system to 60°C, add 34 parts by weight of isophorone diisocyanate dropwise while stirring, and add 2 drops of dibutyltin dilaurate as a catalyst, raise the temperature to 85°C and keep the reaction at this temperature for 3-5 hours; after the reaction is completed, cool to 70°C, slowly add 6.5 parts by weight of hydroxyethyl methacrylate, and keep the reaction at this temperature for 3 hours;

[0028] S2. Preparation of preemulsion

[0029] The polyurethane prepolymer system from step S1 was cooled to 40°C, and 7.5 parts by weight of triethylamine were added to neutralize the reaction. Then, under high-speed stirring, 400 parts by weight of deionized water were slowly added to the system to perform high-speed shear emulsification, thus obtaining the product.

[0030] S3. Preparation of acrylate monomer mixture

[0031] The following mixture is prepared by thoroughly mixing 15 parts by weight of methyl methacrylate, 7 parts by weight of glycidyl methacrylate, 14 parts by weight of lauryl acrylate, 2 parts by weight of acrylic acid, and 2 parts by weight of N-(4-vinyl)-acetamide.

[0032] S4. Preparation of dispersion

[0033] Dissolve 0.5 parts by weight of potassium persulfate in 10 parts by weight of deionized water to form an initiator aqueous solution. Then, take one-third of the solution and add it to the pre-emulsion. Raise the temperature to 75°C and then add the acrylate monomer mixture and the remaining initiator aqueous solution over 3 hours. After the addition is complete, continue to keep the temperature high for 2 hours. After the reaction is complete, cool to room temperature to obtain the final product.

[0034] Furthermore, in step S2, the temperatures of each section of the extruder are set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, and Die head: 275~280℃.

[0035] The present invention further provides an antistatic PET base film for preparing polarizer release films, prepared by the method described above.

[0036] This invention achieves highly uniform orientation of molecular chains in the plane by introducing a rigid comonomer containing a pyridine ring and modified PET with intercalated montmorillonite, in synergy with a three-stage stretching process. This effectively reduces optical anisotropy and meets the requirements of precision optical inspection of polarizers.

[0037] The addition of montmorillonite and modified SiO2 filler to modified PET provides rigidity, improves the heat resistance of the film, and ensures dimensional stability during polarizer processing and use.

[0038] The terpolymer grafted onto the surface of modified SiO2 filler improves the dispersibility of the filler in the PET matrix, greatly enhances the interfacial bonding between the filler and the matrix, and ensures the high light transmittance and low haze optical properties of the PET film. On the other hand, the abundant active sites can form stronger chemical bonds or hydrogen bonds, thereby enhancing the interaction with the antistatic agent coating and improving the adhesion of the antistatic agent coating.

[0039] The antistatic coating solution is formulated with a water-based hydroxy acrylate-polyurethane dispersion, an antistatic agent, and other additives. The resulting antistatic coating is thin and has minimal impact on the optical properties of the base film. The formulation includes an ionic liquid antistatic agent, which imparts antistatic properties to the film. Furthermore, the water-based hydroxy acrylate-polyurethane dispersion is produced by free radical polymerization of an unsaturated double-bond-terminated polyurethane prepolymer with acrylate monomers under an initiator. The water-based resin contains epoxy groups and long-chain alkyl groups that match the surface-modified fillers of the base film. During curing, this process simultaneously achieves high-strength cross-linking within the coating and chemical bonding between the coating and the base film interface. This solves the problems of insufficient adhesion, easy migration, and poor durability of conventional coating solutions on inert PET surfaces, resulting in long-lasting and stable antistatic performance without affecting the optical properties of the base film. The active sites, such as epoxy groups, in the coating that match the modified fillers, also exhibit stronger chemical bonds or hydrogen bonds with the release agent, enhancing adhesion and ensuring the adhesion of the coating to the PET base film, as well as subsequent coatings and release agents.

[0040] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention, through material modification and process improvement, specifically uses optical-grade PET chips as the main material, adds modified PET with a specific structure and modified SiO2 filler, and prepares films through co-extrusion casting and a unique three-stage stretching process. The modified PET, by introducing 2-(pyridin-3-yl) terephthalic acid comonomer and ionic liquid intercalated montmorillonite, improves the rigidity and heat resistance of the molecular chains and provides heterogeneous nucleation sites; the modified SiO2 filler, through surface grafting of terpolymers, achieves good compatibility with the matrix and internal lubrication; the three-stage stretching sequence of "transverse-longitudinal-transverse" and progressively increasing temperature control synergistically regulate the orientation and crystallization of the molecular chains; then, an antistatic coating liquid is coated on the film surface, resulting in a base film with low alignment angle, low transverse thermal shrinkage rate, and high surface adhesion, while maintaining the high light transmittance and low haze characteristics of optical-grade polyester films, and endowing the film with certain antistatic properties, making it particularly suitable for manufacturing release films for high-end polarizers. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] The raw materials used in this application are mostly bulk products that can be purchased on the market. The sources and models of some products are as follows:

[0044]

[0045] Example: An antistatic PET base film for preparing polarizer release films

[0046] S1. Weigh and measure the optical-grade PET chips, modified PET, and modified SiO2 filler, place them in a high-speed mixer and mix them, then dry them under vacuum.

[0047] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0048] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8 times; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6 times; perform a second transverse stretching on the longitudinally stretched film at 125℃ with a stretching ratio of 2.5 times; the three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5 times.

[0049] S4. Heat-set the stretched film at 190°C for 15 seconds, slowly cool it down to 150°C and hold it for 30 minutes, then cool it to room temperature, coat the film surface with an antistatic coating liquid, dry it at 100~120°C, and finally perform corona treatment; then pull and wind it up.

[0050] The preparation methods for some of the raw materials used in the above experiments are as follows:

[0051] 1. The modified PET is prepared by the following method:

[0052] 1) Add sodium montmorillonite and deionized water to a beaker, sonicate to disperse it evenly, then transfer it to a water bath and heat it to 60-70℃. While stirring, slowly add 20% by weight of 1-carboxyethyl-3-methylimidazolium chloride of sodium montmorillonite. After the addition is complete, keep it at the temperature for 2-3 hours, filter, wash with water, dry, and grind to obtain 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite.

[0053] 2) Add ethylene glycol and 2-(pyridin-3-yl)terephthalic acid to the reactor, add tetrabutyl titanate as a catalyst, raise the temperature to 200~230℃ for esterification reaction, add terephthalic acid after 2~3h, raise the temperature to 250℃, react for 2~4h, add antimony glycol ethylene as a catalyst, control the pressure in the reactor at 0.3 MPa, raise the temperature to 270℃ and react for 2~3h; after the reaction is completed, allow the material to cool naturally and discharge to obtain poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester; then mix it with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite in a high-speed mixer, melt blend and granulate through a twin-screw extruder to obtain the final product.

[0054] In the process of preparing the modified PET, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9:1.

[0055] 2. The preparation steps of the modified SiO2 filler are as follows:

[0056] 1) A certain amount of nano-SiO2 particles were first activated with potassium hydroxide, then dispersed in deionized water and an equal mass of KH570 was added. The mixture was stirred at 50°C for 24 hours, filtered, washed, dried and ground to obtain KH570 modified SiO2 powder.

[0057] 2) KH570 modified SiO2 powder was dispersed in THF, and lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide were added in sequence. AIBN of 1% of the total monomer mass was added as an initiator. The reaction was carried out at 70℃ under nitrogen protection for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times with THF to remove the homopolymer. After vacuum drying, the modified SiO2 filler was obtained.

[0058] In the preparation of the modified SiO2 filler, the molar ratio of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide is 60:20:20; and the sum of their masses is 100% of the KH570 modified SiO2 powder.

[0059] 3. The preparation process of the antistatic coating liquid is as follows:

[0060] First, an aqueous hydroxy acrylate-polyurethane dispersion is prepared, including the following steps:

[0061] S1. Preparation of polyurethane prepolymer

[0062] Add 60 parts by weight of polybutylene adipate diol and 10 parts by weight of dimethylolpropionic acid to a reaction flask, add 30 parts by weight of N-methylpyrrolidone as a solvent, purge with nitrogen, heat to 80°C and stir to mix evenly, cool the system to 60°C, add 34 parts by weight of isophorone diisocyanate dropwise while stirring, and add 2 drops of dibutyltin dilaurate as a catalyst, raise the temperature to 85°C and keep the reaction at this temperature for 3-5 hours; after the reaction is completed, cool to 70°C, slowly add 6.5 parts by weight of hydroxyethyl methacrylate, and keep the reaction at this temperature for 3 hours;

[0063] S2. Preparation of preemulsion

[0064] The polyurethane prepolymer system from step S1 was cooled to 40°C, and 7.5 parts by weight of triethylamine were added to neutralize the reaction. Then, under high-speed stirring, 400 parts by weight of deionized water were slowly added to the system to perform high-speed shear emulsification, thus obtaining the product.

[0065] S3. Preparation of acrylate monomer mixture

[0066] The following mixture is prepared by thoroughly mixing 15 parts by weight of methyl methacrylate, 7 parts by weight of glycidyl methacrylate, 14 parts by weight of lauryl acrylate, 2 parts by weight of acrylic acid, and 2 parts by weight of N-(4-vinyl)-acetamide.

[0067] S4. Preparation of dispersion

[0068] Dissolve 0.5 parts by weight of potassium persulfate in 10 parts by weight of deionized water to form an initiator aqueous solution. Then, take one-third of the solution and add it to the pre-emulsion. Raise the temperature to 75°C and then add the acrylate monomer mixture and the remaining initiator aqueous solution over 3 hours. After the addition is complete, continue to keep the temperature high for 2 hours. After the reaction is complete, cool to room temperature to obtain the final product.

[0069] Weigh out 75 g of waterborne hydroxy acrylate-polyurethane dispersion, 10 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 2 g of hydrophilic aliphatic polyisocyanate, 1 g of KH560, 0.3 g of polyether-modified polysiloxane, and 11.7 g of deionized water.

[0070] Using the above-mentioned raw materials and preparation process, the following specific embodiments are obtained:

[0071] Example 1 S1: Weigh 100 parts by weight of optical grade PET chips, 8 parts by weight of modified PET, and 3 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0072] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0073] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8 times; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6 times; perform a second transverse stretching on the longitudinally stretched film at 125℃ with a stretching ratio of 2.5 times; the three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5 times.

[0074] S4. Heat-set the stretched film at 190℃ for 15 seconds, slowly cool it to 150℃ and hold for 30 minutes, then cool it to room temperature. Coat the film surface with an antistatic coating liquid with a wet coating amount of 5 g / m². 2 Dry at 100~120℃, and finally undergo corona treatment; then traction and winding.

[0075] Example 2 S1: Weigh 100 parts by weight of optical grade PET chips, 8 parts by weight of modified PET, and 3 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0076] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0077] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8 times; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6 times; perform a second transverse stretching on the longitudinally stretched film at 125℃ with a stretching ratio of 2.5 times; the three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5 times.

[0078] S4. Heat-set the stretched film at 190℃ for 15 seconds, slowly cool it to 150℃ and hold for 30 minutes, then cool it to room temperature. Coat the film surface with an antistatic coating liquid with a wet coating amount of 10 g / m². 2 Dry at 100~120℃, and finally undergo corona treatment; then traction and winding.

[0079] Example 3 S1: Weigh 100 parts by weight of optical grade PET chips, 8 parts by weight of modified PET, and 3 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0080] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0081] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8 times; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6 times; perform a second transverse stretching on the longitudinally stretched film at 125℃ with a stretching ratio of 2.5 times; the three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5 times.

[0082] S4. Heat-set the stretched film at 190℃ for 15 seconds, slowly cool it to 150℃ and hold for 30 minutes, then cool it to room temperature. Coat the film surface with an antistatic coating liquid with a wet coating amount of 15 g / m².2 Dry at 100~120℃, and finally undergo corona treatment; then traction and winding.

[0083] Example 4 S1: Weigh 100 parts by weight of optical grade PET chips, 12 parts by weight of modified PET, and 5 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0084] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0085] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8 times; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6 times; perform a second transverse stretching on the longitudinally stretched film at 125℃ with a stretching ratio of 2.5 times; the three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5 times.

[0086] S4. Heat-set the stretched film at 190℃ for 15 seconds, slowly cool it to 150℃ and hold for 30 minutes, then cool it to room temperature. Coat the film surface with an antistatic coating liquid with a wet coating amount of 10 g / m². 2 Dry at 100~120℃, and finally undergo corona treatment; then traction and winding.

[0087] Example 5 S1: Weigh 100 parts by weight of optical grade PET chips, 15 parts by weight of modified PET, and 8 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0088] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0089] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8 times; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6 times; perform a second transverse stretching on the longitudinally stretched film at 125℃ with a stretching ratio of 2.5 times; the three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5 times.

[0090] S4. Heat-set the stretched film at 190℃ for 15 seconds, slowly cool it to 150℃ and hold for 30 minutes, then cool it to room temperature. Coat the film surface with an antistatic coating liquid with a wet coating amount of 10 g / m². 2 Dry at 100~120℃, and finally undergo corona treatment; then traction and winding.

[0091] Comparative Example 1

[0092] Compared to Example 4, no modified PET was added; its proportion was replaced by an equal amount of ordinary optical-grade PET chips.

[0093] Comparative Example 2

[0094] Compared to Example 4, ungrafted KH570-SiO2 powder was used instead of modified SiO2 filler.

[0095] Comparative Example 3

[0096] Compared to Example 4, no antistatic coating was applied.

[0097] Comparative Example 4

[0098] Compared to Example 4, the antistatic coating liquid used was a commercially available antistatic liquid (PEDOT / PSS dispersion slurry, Heraeus's Clevios™ series).

[0099] In the above preparation process, the thickness of the film is controlled at 40±2 μm; the obtained film is subjected to the following performance tests, and the results are recorded in Table 1.

[0100] Orientation angle: The orientation angle of the thin film at 50 mm intervals was measured using an automatic ellipsometry, and the maximum value was recorded.

[0101] Heat shrinkage rate: The film was placed in a 150°C forced-air oven for 30 minutes, and the change in transverse (TD) dimensions was measured.

[0102] Transmittance and haze: measured using a haze meter according to GB / T 2410-2008.

[0103] Adhesion: The cross-cut test was performed on the surface of the cured base film. 0B is the worst and 5B is the best.

[0104] Residual adhesion: Coated with silicone release agent and tested according to GB / T25256-2010 standard.

[0105] Surface resistivity: GB / T 1410-2006, test voltage 500V, charging time 60s, environmental conditions 23°C / 50% RH.

[0106] Table 1

[0107]

[0108] Comparing Examples 1-3, the increased antistatic agent coating amount resulted in enhanced conductivity and a slight decrease in optical properties; however, due to the good adhesion between the coating and the base film, the adhesion remained at a high level (4B-5B). Comparing Examples 2 with Examples 4 and 5, the coating amount was fixed at 10 g / m². 2 Increasing the amount of modified PET and modified SiO2 fillers, although causing a slight decrease in light transmittance due to filler scattering, significantly improved the dimensional stability of the film (heat shrinkage rate decreased to 0.9%) and further reduced the alignment angle, demonstrating the decisive role of matrix modification in the core optical and thermal properties. Observing Comparative Examples 1 and 2, the modified PET and modified SiO2 fillers in the system affected the alignment angle and surface adhesion of the film materials, respectively. The significant decrease in adhesion in Comparative Example 2 was due to the lack of interfacial interaction and abundant active sites of the modified SiO2 filler, leading to slight agglomeration of the filler in the base film, resulting in uneven coating of the antistatic coating liquid and decreased adhesion; consequently, the stability of the release agent on its surface weakened, and the residual adhesion decreased significantly. Comparative Example 4, coated with a common antistatic coating liquid, showed significant antistatic effect, but the adhesion to PET was weak. Since the antistatic coating serves as an intermediate layer between the base film and the release agent, it needs to have good adhesion to both the base film and the release agent. The waterborne hydroxyl acrylate-polyurethane dispersion acts as a crucial bridge between these two components. Commercially available antistatic liquids cannot establish this chemical bridge, resulting in weak interfacial adhesion and consequently, unstable release agent coating and decreased residual adhesion. Comparative Example 3, without an antistatic coating, still maintains high adhesion to the release agent due to the presence of modified SiO2 filler on its base film surface, which provides abundant active sites. However, its antistatic performance is significantly reduced due to the lack of an antistatic coating.

[0109] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing an antistatic PET base film for preparing a polarizer release film, characterized in that, Includes the following steps: S1. Weigh 100 parts of optical grade PET chips, 8-15 parts of modified PET, and 3-8 parts of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum. S2. The dried mixture is fed into a single screw extruder, and the extrusion temperature is set to 255~285℃. After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet. S3. Preheat the cast film to 90℃, perform a first transverse stretching with a stretching ratio of 1.5~2.5 times and a temperature of 95~105℃; then perform a longitudinal stretching with a stretching ratio of 3.2~5 times and a temperature of 105~115℃; perform a second transverse stretching on the longitudinally stretched film with a stretching ratio of 2.5~3.5 times and a temperature of 120~135℃; the three-stage stretching temperature increases progressively, with a total transverse stretching ratio of 3.75~6 times; S4. The stretched film is heat-set at 190~220℃ for 5~15s, slowly cooled to 150℃ and held for 10~30min, then cooled to room temperature. An antistatic coating is applied to the film surface, dried at 100~120℃, and finally corona treated; then pulled and wound up; wherein, The modified PET is prepared by introducing 2-(pyridin-3-yl) terephthalic acid to replace part of the terephthalic acid during the PET polymerization process, and then blending it with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite and melt extruding it after polymerization. The modified SiO2 filler is obtained by free radical polymerization of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide terpolymer grafted onto the surface of KH570 modified SiO2. The antistatic coating liquid comprises 70-80 wt% aqueous hydroxy acrylate-polyurethane dispersion, 5-15 wt% ionic liquid antistatic agent, 1-3 wt% curing agent, 0.5-2 wt% accelerator, 0.1-0.5 wt% wetting and leveling agent, and the balance being deionized water; The ionic liquid antistatic agent is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt; The preparation process of the aqueous hydroxy acrylate-polyurethane dispersion is as follows: 1) Preparation of polyurethane prepolymer Add 60 parts by weight of polybutylene adipate diol and 10 parts by weight of dimethylolpropionic acid to a reaction flask, add 30 parts by weight of N-methylpyrrolidone as a solvent, purge with nitrogen, heat to 80°C and stir to mix evenly, cool the system to 60°C, add 34 parts by weight of isophorone diisocyanate dropwise while stirring, and add 2 drops of dibutyltin dilaurate as a catalyst, raise the temperature to 85°C and keep the reaction at this temperature for 3-5 hours; after the reaction is completed, cool to 70°C, slowly add 6.5 parts by weight of hydroxyethyl methacrylate, and keep the reaction at this temperature for 3 hours; 2) Preparation of preemulsion The polyurethane prepolymer system from step S1 was cooled to 40°C, and 7.5 parts by weight of triethylamine were added to neutralize the reaction. Then, under high-speed stirring, 400 parts by weight of deionized water were slowly added to the system to perform high-speed shear emulsification, thus obtaining the product. 3) Preparation of acrylate monomer mixture The following mixture is prepared by thoroughly mixing 15 parts by weight of methyl methacrylate, 7 parts by weight of glycidyl methacrylate, 14 parts by weight of lauryl acrylate, 2 parts by weight of acrylic acid, and 2 parts by weight of N-(4-vinyl)-acetamide. 4) Preparation of dispersion Dissolve 0.5 parts by weight of potassium persulfate in 10 parts by weight of deionized water to form an initiator aqueous solution. Then, take one-third of the solution and add it to the pre-emulsion. Raise the temperature to 75°C and then add the acrylate monomer mixture and the remaining initiator aqueous solution over 3 hours. After the addition is complete, continue to keep the temperature high for 2 hours. After the reaction is complete, cool to room temperature to obtain the final product.

2. The method for preparing an antistatic PET base film for preparing a polarizer release film according to claim 1, characterized in that, The preparation process of the 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is as follows: Add sodium montmorillonite and deionized water to a beaker, sonicate to disperse it evenly, then transfer it to a water bath and heat it to 60-70℃. While stirring, slowly add 20% by weight of 1-carboxyethyl-3-methylimidazolium chloride of sodium montmorillonite. After the addition is complete, keep it at the temperature for 2-3 hours, filter, wash with water, dry, and grind to obtain the final product.

3. The method for preparing an antistatic PET base film for preparing a polarizer release film according to claim 1, characterized in that, The modified PET is prepared by the following method: Ethylene glycol and 2-(pyridin-3-yl)terephthalic acid were added to a reactor, and tetrabutyl titanate was added as a catalyst. The temperature was raised to 200-230℃ for esterification. After reacting for 2-3 hours, terephthalic acid was added, and the temperature was raised to 250℃. After reacting for 2-4 hours, antimony glycolate was added as a catalyst. The pressure in the reactor was controlled at 0.3 MPa, and the temperature was raised to 270℃ for 2-3 hours. After the reaction was completed, the product was discharged after natural cooling to obtain poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester. Then, it was mixed with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite in a high-speed mixer until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder to obtain the final product.

4. The method for preparing an antistatic PET base film for preparing a polarizer release film according to claim 3, characterized in that, The molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:10~20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester) to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9~9.5:0.5~1.

5. The method for preparing an antistatic PET base film for preparing a polarizer release film according to claim 1, characterized in that, The preparation steps of the modified SiO2 filler are as follows: 1) A certain amount of nano-SiO2 particles were first activated with potassium hydroxide, then dispersed in deionized water and an equal mass of KH570 was added. The mixture was stirred at 50°C for 24 hours, filtered, washed, dried and ground to obtain KH570 modified SiO2 powder. 2) KH570 modified SiO2 powder was dispersed in THF, and lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide were added in sequence. AIBN of 1% of the total monomer mass was added as an initiator. The reaction was carried out at 70℃ under nitrogen protection for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times with THF to remove the homopolymer. After vacuum drying, the modified SiO2 filler was obtained.

6. The method for preparing an antistatic PET base film for preparing a polarizer release film according to claim 5, characterized in that, The molar ratio of lauryl acrylate, glycidyl methacrylate, and N-(4-vinylphenyl)acetamide is 50~70:15~25:15~25; the sum of their masses is 80%~120% of the KH570 modified SiO2 powder.

7. The method for preparing an antistatic PET base film for preparing a polarizer release film according to claim 1, characterized in that, The curing agent in the antistatic coating liquid is a hydrophilic aliphatic polyisocyanate; the accelerator is KH-560; the wetting and leveling agent is a polyether-modified polysiloxane; and the wet coating amount of the antistatic coating liquid is 5~15 g / m². 2 .

8. An antistatic PET base film for preparing a polarizer release film, prepared by any one of claims 1 to 7.

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